1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a TFT (Thin Film Transistor) LCD (Liquid Crystal Display) having a large aperture ratio.
2. Background of the Related Art
Referring to FIG. 1A, an AMLCD (Active Matrix Liquid Crystal Display Device) used in a portable TV or a notebook computer, or the like is provided with a plurality of scanning lines 10 and signal lines 17 crossing each other, and pixel regions defined by the scanning lines 10 and the signal lines 17. These are TFTs at parts where the scanning lines 10 and the signal lines are crossed; and pixel electrodes (dashed lines in the drawing) in the pixel regions for displaying a desired picture when a voltage is applied to the scanning lines 10, to switch the TFT, and to transmit a picture signal provided to the signal lines 17 to the pixel electrodes.
Referring to FIG. 1B showing a section across line A–A′, the AMLCD is provided with a gate electrode 11 on a transparent substrate 7, and a gate insulating layer 13 on the gate electrode 11. There is a channel layer 15 and an ohmic contact layer 16 of amorphous silicon a-Si on the gate insulating layer 13, and source/drain electrodes 17a and 17b on the ohmic contact layer 16. There is a protection layer 19 on an entire surface of the source/drain electrodes 17a and 17b, a contact hole 20 in the protection layer 19. The pixel electrode 21 and the drain electrode 17b are connected through the contact hole 20. In the drawing, Cgs denotes a capacitance between the gate electrode and the source electrode, Cgd denotes a capacitance between the gate electrode and the drain electrode. The Ccross denotes a capacitance in overlap regions of the scanning lines and the signal lines. The Cgs, Cgd, and Ccross are parameters influencing to an accumulated capacitance (not shown), as well as ΔVp (change in offset voltage) and ΔVpxl (change in pixel voltage). In the related art LCD, if there is a misalignment between the scanning line 10 and the signal line 17, minute variations of Cds and Cgd give influence to ΔVp and ΔVpxl, making flicker worse and causing non-uniform luminance, that deteriorates a picture quality. And, in a divided exposure for a large sized screen, the increased deviations of Cgs and Cgd caused by poor adjustment between shots worsens the foregoing problem, to impede providing a large sized LCD screen, and, since the TFT is formed on an extension line of the scanning line, to reduce an aperture ratio of the device.